1. Field of the Invention
The present invention relates to a diagnostic method and a diagnostic apparatus adopted to detect a failure in a cell among cells constituting a battery pack.
2. Description of the Related Art
The individual capacities and the like of a plurality of cells constituting a battery pack change in correspondence to the charge/discharge current during a charge/discharge and thus, the inconsistency among the individual cell capacities cannot be detected accurately during the charge/discharge. As a solution, a battery pack diagnostic apparatus has been disclosed in the known art (see Japanese Laid-Open Patent Publication No. H11-149944), which measures the cell voltages at a vehicle startup or a charge start when the cells are in a stable state and detects a faulty cell based upon the measured cell voltage values.
However, the battery pack diagnostic apparatus in the prior art, which is capable of performing diagnosis on the battery pack only at a vehicle startup or at a charge start, cannot detect a cell failure occurring while the battery pack is in normal use, such as while the vehicle is running. Thus arises a problem in that appropriate measures cannot be taken when such a cell failure occurs.
An object of the present invention is to provide a battery pack diagnostic method and a battery pack diagnostic apparatus that enable accurate diagnosis on any failure occurring in the battery pack while the battery pack is in normal use.
The battery pack diagnostic apparatus according to the present invention performs diagnosis on a plurality of cells constituting a battery pack. The battery pack diagnostic apparatus comprises a current measuring instrument that measures the current flowing through the battery pack, a voltage measuring instrument that measures a cell voltage at the terminals of each cell, a measurement control device that starts the cell voltage measurement by the voltage measuring instrument when the absolute value of the current flowing through the battery pack measured by the current measuring instrument has sustained a level equal to or lower than a predetermined value over a specific length of time and a faulty cell detection device that detects a faulty cell based upon measured cell voltage values at the individual cells.
Alternatively, the battery pack diagnostic apparatus according to the present invention may comprise a current measuring instrument that measures the current flowing through the battery pack, a voltage measuring instrument that measures cell voltage at the terminals of each cell, a measurement control device that starts the cell voltage measurement by the voltage measuring instrument when the absolute value of the current flowing through the battery pack measured by the current measuring instrument has sustained a level equal to or lower than a predetermined value over the specific length of time and a faulty cell detection device that detects a faulty cell based upon the measured cell voltage values at the individual cells detected by the voltage measuring instrument, and the measurement control device may start the cell voltage measurement anew if the absolute value of the current flowing through the battery pack exceeds the predetermined value during the cell voltage measurement by the voltage measuring instrument or if the absolute value of the difference between the maximum value and the minimum value of the current flowing through the battery pack exceeds a predetermined value, to perform diagnosis on the plurality of cells constituting the battery pack.
In the battery pack diagnostic method according to the present invention, a cell voltage is measured at the terminals of each cell when the absolute value of the current flowing through the battery pack has sustained a level equal to or lower than a predetermined value over a specific length of time and a faulty cell is detected based upon measured cell voltages. The method enables a diagnosis to be performed on a plurality of cells constituting the battery pack.
Alternatively, in the battery pack diagnostic method comprising, measuring a cell voltage anew if the absolute value of the current flowing through the battery pack exceeds a predetermined value during a cell voltage measurement or if the absolute value of the difference between the maximum value and the minimum value of the current flowing through the battery pack exceeds a predetermined value during a cell voltage measurement, and to detect a faulty cell based upon the measured cell voltages.